/**
 * Copyright (C) 2009-2011 Couchbase, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALING
 * IN THE SOFTWARE.
 */

package com.nepxion.thunder.cluster.loadbalance.consistenthash.ketama;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.zip.CRC32;

/**
 * Known hashing algorithms for locating a server for a key. Note that all hash
 * algorithms return 64-bits of hash, but only the lower 32-bits are
 * significant. This allows a positive 32-bit number to be returned for all
 * cases.
 */
public enum DefaultHashAlgorithm implements HashAlgorithm {

    /**
     * Native hash (String.hashCode()).
     */
    NATIVE_HASH,

    /**
     * CRC_HASH as used by the perl API. This will be more consistent both
     * across multiple API users as well as java versions, but is mostly likely
     * significantly slower.
     */
    CRC_HASH,

    /**
     * FNV hashes are designed to be fast while maintaining a low collision
     * rate. The FNV speed allows one to quickly hash lots of data while
     * maintaining a reasonable collision rate.
     *
     * @see <a href="http://www.isthe.com/chongo/tech/comp/fnv/">fnv
     *      comparisons</a>
     * @see <a href="http://en.wikipedia.org/wiki/Fowler_Noll_Vo_hash">fnv at
     *      wikipedia</a>
     */
    FNV1_64_HASH,

    /**
     * Variation of FNV.
     */
    FNV1A_64_HASH,

    /**
     * 32-bit FNV1.
     */
    FNV1_32_HASH,

    /**
     * 32-bit FNV1a.
     */
    FNV1A_32_HASH,

    /**
     * MD5-based hash algorithm used by ketama.
     */
    KETAMA_HASH;

    private static final long FNV_64_INIT = 0xcbf29ce484222325L;
    private static final long FNV_64_PRIME = 0x100000001b3L;

    private static final long FNV_32_INIT = 2166136261L;
    private static final long FNV_32_PRIME = 16777619;

    private static MessageDigest md5Digest = null;

    static {
        try {
            md5Digest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException("MD5 not supported", e);
        }
    }

    /**
     * Compute the hash for the given key.
     * @param k the object key
     * @return a positive integer hash
     */
    public long hash(final String k) {
        long rv = 0;
        int len = k.length();
        switch (this) {
            case NATIVE_HASH:
                rv = k.hashCode();
                break;
            case CRC_HASH:
                // return (crc32(shift) >> 16) & 0x7fff;
                CRC32 crc32 = new CRC32();
                crc32.update(KeyUtil.getKeyBytes(k));
                rv = (crc32.getValue() >> 16) & 0x7fff;
                break;
            case FNV1_64_HASH:
                // Thanks to pierre@demartines.com for the pointer
                rv = FNV_64_INIT;
                for (int i = 0; i < len; i++) {
                    rv *= FNV_64_PRIME;
                    rv ^= k.charAt(i);
                }
                break;
            case FNV1A_64_HASH:
                rv = FNV_64_INIT;
                for (int i = 0; i < len; i++) {
                    rv ^= k.charAt(i);
                    rv *= FNV_64_PRIME;
                }
                break;
            case FNV1_32_HASH:
                rv = FNV_32_INIT;
                for (int i = 0; i < len; i++) {
                    rv *= FNV_32_PRIME;
                    rv ^= k.charAt(i);
                }
                break;
            case FNV1A_32_HASH:
                rv = FNV_32_INIT;
                for (int i = 0; i < len; i++) {
                    rv ^= k.charAt(i);
                    rv *= FNV_32_PRIME;
                }
                break;
            case KETAMA_HASH:
                byte[] bKey = computeMd5(k);
                rv = ((long) (bKey[3] & 0xFF) << 24)
                        | ((long) (bKey[2] & 0xFF) << 16)
                        | ((long) (bKey[1] & 0xFF) << 8)
                        | (bKey[0] & 0xFF);
                break;
            default:
                assert false;
        }
        return rv & 0xffffffffL; /* Truncate to 32-bits */
    }

    /**
     * Get the md5 of the given key.
     * @param k the object key
     * @return byte[]
     */
    public static byte[] computeMd5(String k) {
        MessageDigest md5;
        try {
            md5 = (MessageDigest) md5Digest.clone();
        } catch (CloneNotSupportedException e) {
            throw new RuntimeException("clone of MD5 not supported", e);
        }
        md5.update(KeyUtil.getKeyBytes(k));
        return md5.digest();
    }
}